Exemplary embodiments of the inventive concepts relate to semiconductor devices and, more particularly, to a nonvolatile random access memory including a reference cell and a data read method thereof.
In general, semiconductor memory devices are classified into volatile memory devices and nonvolatile memory devices. Volatile memory devices have high read/write speed but lose their stored data when their power supplies are interrupted. On the other hand, nonvolatile memory devices retain their stored data even when their power supplies are interrupted. Therefore, the nonvolatile memory devices are used to store data that must be retained regardless of power supply.
Recently, there is an increasing demand for nonvolatile semiconductor memory devices that are capable of implementing high density and high capacity. Flash memories mainly used in mobile electronic devices are representative memories that meet the demand. However, studies have been extensively made on random-access nonvolatile memory devices with improved performance. Such memory devices include, for example, ferroelectric random access memory (FRAM) using a ferroelectric capacitor, magnetic RAM (MRAM) using a tunneling magnetoresistive (TMR) layer, phase change memory device using chalcogenide alloys, resistive RAM (RRAM) using a variable resistance material layer as a data storage medium, and the like.
The above-mentioned nonvolatile memories include reference cells for identifying data stored in memory cells. Data stored in a memory cell may be precisely sensed with reference to data stored in a reference cell. Precision of a reference signal generated from a reference cell is required for high data integrity. However, a reference signal provided by reference cells may vary depending on various factors, which causes a read error.